Electrochemical energy stores, such as lithium-ion batteries, are widely used in many daily applications. By way of example, they are used in computers, such as laptops, cell phones, smart phones and further applications. Such batteries also afford advantages for the currently heavily promoted electrification of vehicles, such as motor vehicles, for example for electric vehicles or hybrid vehicles.
By way of example, lithium-ion batteries, for example for the automotive field of use, often comprise a plurality of individual battery cells. In order to increase the voltage or current level, these cells are connected up to one another in parallel or in series and combine mechanically to form modules. A battery management system is additionally used to monitor the battery and is intended to allow not only safety monitoring but also the longest possible life.
In order to increase life, for example, it is known practice to match the state of charge of the battery cells to one another. This process is also referred to as cell balancing. By way of example, the document US 2011/0163720 A1 discloses a motor vehicle that has an electric motor, a battery, an interface for a driver and one or more control units. In this case, when there is an imbalance in the states of charge of battery cells in the battery, a warning needs to be output to the interface for the driver and the states of charge need to be aligned on the basis of a response. In this case, the states of charge can be aligned on the basis of the self-discharge rate, for example.
The document JP 2008-295250 additionally describes a method for monitoring the uniformity of the states of charge of battery cells. In this case, the cell voltages of the battery cells are ascertained during charging and during discharging and a control unit selectively discharges battery cells in a discharge circuit.